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From GitBox <...@apache.org>
Subject [GitHub] [cassandra] clohfink commented on a change in pull request #402: New/virtualtables
Date Fri, 14 Feb 2020 16:26:33 GMT
clohfink commented on a change in pull request #402: New/virtualtables
URL: https://github.com/apache/cassandra/pull/402#discussion_r379513902
 
 

 ##########
 File path: doc/source/new/virtualtables.rst
 ##########
 @@ -0,0 +1,586 @@
+.. Licensed to the Apache Software Foundation (ASF) under one
+.. or more contributor license agreements.  See the NOTICE file
+.. distributed with this work for additional information
+.. regarding copyright ownership.  The ASF licenses this file
+.. to you under the Apache License, Version 2.0 (the
+.. "License"); you may not use this file except in compliance
+.. with the License.  You may obtain a copy of the License at
+..
+..     http://www.apache.org/licenses/LICENSE-2.0
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+
+Virtual Tables
+--------------
+
+Apache Cassandra 4.0 implements virtual tables (`CASSANDRA-7622
+<https://issues.apache.org/jira/browse/CASSANDRA-7622>`_).
+
+Definition
+^^^^^^^^^^
+
+A virtual table is a table that is backed by an API instead of data explicitly managed and
stored as SSTables. Apache Cassandra 4.0 implements a virtual keyspace interface for virtual
tables. Virtual tables are specific to each node. 
+
+Objective
+^^^^^^^^^
+
+A virtual table could have several uses including:
+
+- Expose JMX data/metrics through CQL
+- Expose YAML configuration information
+- Expose other MBean data
+ 
+How  are Virtual Tables different from regular tables?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Virtual tables and virtual keyspaces are quite different from regular tables and keyspaces
respectively such as:
+
+- Virtual tables are read-only 
+- Virtual tables are not replicated
+- Virtual tables have no associated SSTables
+- Consistency level of the queries sent virtual tables are ignored
+- Virtual tables are managed by Cassandra and a user cannot run  DDL to create new virtual
tables or DML to modify existing virtual tables
+- Virtual tables are created in special keyspaces and not just any keyspace
+- All existing virtual tables use LocalPartitioner
 
 Review comment:
   Not even sure we should say thats different then regular tables since many system tables
use LocalPartitioner and are non-replicated. But we should definitely highlight that they
these tables are local only and non distributed

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